Process of treating and purifying hydrocarbon lubricating oils



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Patented Den. 3, 1929 ETED STATES PTENT FICE WILLIAM M. STRATFORD, OF PORT ARTHUR, TEXAS, ASSIGNOR, BY MESNE ASSIGN MENTS, TO THE TEXAS COMPANY, OF NEW YORK, N. Y., A CORPORATION OF DELA- WARE PROCESS OF TREATING AND PURIFYING HYDIROCARBON LUBRICATING OILS No Drawing.

This invention relates to a process of treat ing and purifying hydrocarbon lubricating oils and has particular reference to a process comprising the economical production of lubricating oils of a high degree of purity and stability.

An important object of the invention is a complete elimination of acidic constituents from hydrocarbon lubricating oil.

Another object of the invention is to pro vide a process for the manufacture of lubrieating oils of the highest quality containing relatively small proportions of colored constituents.

A further object of the invention is to manufacture lubricating oils having a high degree of resistance to emulsification With water or with aqueous solutions.

The invention broadly contemplates a process of refining and purifying hydrocarbon lubricating oils which comprises treating the oil with sulfuric acid followed by neutralization with an aqueous alkaline solution or by other means after which the oil is subjected to distillation preferably under reduced pressure in the presence of an alkaline material such as caustic soda or other strong bases.

In the usual refining of hydrocarbon lubrieating oils it is customary to first distill from the crude petroleum a suitable fraction having the desired properties as shown by the flash test, specific gravity, viscosity, etc. This fraction, which Will ordinarily contain certain unstable products such as small quantities of organic acids and tarry constituents, is then treated with concentrated sulfuric acid and, after Washing with an alkaline solution;

constitutes the ordinary marketable grade of hydrocarbon lubrlcatmg 011s. 011s refined by such means, however, may be unsatisfac+ tory from certain standpoints. For example, such oils are usually of a dark color, red or at best a deep reddish yellow. However, oils of a light golden yellow color are in the greatest demand and command the best prices on the market and are also much purer than the darker colored oils, and it is therefore usually necessary to filter the ordinary acid treated lubricating oil through large quanti- Application filed June 14,

ties of fullers earth in order to remove enough of the color and impurities to produce an oil which is reasonably satisfactory. Filtration, especially to the excessive degree usually required to produce. a satisfactory color and purity in the filtered oil, is objectable due to the very considerable expense incurred thereby.

A further objection to oils treated and puri lied in the usual manner described above is their tendency to form emulsions with Water and with aqueous solutions, particularly when ennployed in the lubrication of steam turbines and under like conditions. It has been found that this tendency is to a great extent due to the presence of minute quantities of oil soluble organic acids which are not removable by the usual methods of washing with alkaline solutions employed in refining processes. It may be possible in certain cases to remove these small quantities of acid by filtration through fullers earth but the process is comparatively expensive and does not finally produce products of the highest resistance to emulsification unless carried on to excessive degree.

I have discovered a process of refining hys drocarbon lubricating oils by which the oils are rendered lighter in color than that usually encountered in even the very best grades of highly filtered oils, are much more color stable than any of the oils heretofore in com mon usage, and are substantially free from impurities tending to produce emulsions with Water or aqueous solutions. My invention maybe applied to the refining of lubricating oils from practically any source, such for example as a Pennsylvania paraffin base crude, the so-called mixed base crudes from the Mid Continent field or the naphthene base crudes of the California or Gulf Coastal fields. In

the application of my invention to the refining of lubricating oils from any source the procedure is in general as follows:

The crude petroleum is first subjected to distillation for the removal of lighter fractions corresponding to naphtha, burning oil, gas oil, and the like. After these fractions are taken oil" the lubricating oils, which may be considered to cover all fractions having viscosities in excess of 50 seconds at 109 1*,

(Saybolt Universal), are then distilled over. It is of course necessary that the distillation of the lubricating fractions take place without substantial cracking or decomposition and this is best obtained by carrying 011 the distillation under a high vacuum and with a passage of steam through the body of oil in the still. However, I have found that the use of high vacuum, although desirable, is not absolutely necessary in carrying on the original distillation of the lubricating fractions fromthe crude petroleum. The fractions which are to be refined for the production of lubricants are separated into the required portions with regard to viscosity, flash point, and other properties and are then in condition for acid treatment, while the still residue is available for fuel oil or for the manufacture of asphalt or for any other suitableuse. V

' ollowing the original distillation, the lubricating fractions are subjected to treatment with sulfuric acid in the usual manner, the quantity of acid'varying with the individual characteristics of the fraction distilled but in general ranging from 6 to 40 lbs. of 98% sulfuric acid per barrel of oil. The sludge products resulting from the treatment with aeidare separated and the oil is substantially neutralized by agitation with an excess of an alkaline solution such as soda ash or caustic soda until it gives a normal neutral reaction. In such a condition the oil, although neutral to test with the usual indicators in aqueous solution, actually contains an amount of organic acids usually referred 'to as naphthenic acids, and while much lighter in color than was the case before acid treatment, is still of a red or dark orange color. Up to this point the oil is practically similar to the usual merchantable grade of hydrocarbon lubricating oils prepared in the usual manner. In order to further purify the'oil, removing organic acids, alkali soaps, and coloring matter, the oil following acid treatment is subjected to distillation under high vacuum in the presence of alkaline material,"preferably caustic soda. Oils refined by this process are completely freed from emulsifyingagents and are not only greatly reducedin color but are so purified that the unstable easily oxidized constituents normally contained in even the most highly refined hydrocarbon lubricating oils, are substantially'absent; The step of distillation under high vacuum iirthe presence of alkaline material, after treatment with. sulfuric acid, is consideredof great importaneesince by this means oils of high initial quality and having a high resistance to decomposition from heat and from oxidation, can be produced.

.. In refining lubricating oils from certain types of crude petroleum by means of my invention it may be desirable from an economicstandpoint to avoid distilling the lubrieating fractions twice. In such cases it is preferable to proceed by a modification of the preferred method which has been described before. By this method the lighter fractions such as naphtha and illuminating oils are distilled from the crude and the residual oil is then treated with acid and neutralized in the usual manner. This treated residual oil is then subjected to distillation under high vacuum in the presence of caustic soda or alkali until the lubricating oil fractions are distilled over. The oil remaining undistilled will contain certain alkali residues which will not, however, affect its value for fuel or other purposes for which still residues are usually available.

As previously stated, the final distillation in the presence of alkaline material is desirably carried out under reduced pressure and this particularly applies to the higher boiling and more viscous oils. Steam may advantageously be introduced below the surface of the oil during distillation to aid vaporization and to insure turbulence in the distilling vessel. The degree of vacuum used may be varied, although it will be found in general that a pressure of less than 100 111/111. of mercury is most suitable and, if steam is not also used, a very much lower pressure will be desirable.

Although distillation over alkaline materials has been described above in connection with oils which had been previously treated with sulfuric acid, this step may be embodied in numerous specific applications of the invention. For example, in the ease of such oils as those derived from the Gulf Coastal orudes, it may often be found desirable to distill. the oil in the presence of alkali before acid treatment in order to avoid troublesome emulsions due to the initial content of natural acidic constituents of the oil which would tend to form permanent emulsions during acid treatment and neutralization.

The quantity of alkali necessary during distillation will of course vary to some degree with the nature of the oil, care being taken at all times to provide a large excess over the quantity required for neutralizing the acidic constituents. For example, an acid treated and substantially neutralized lubricating oil derived from Gulf Coastal crude may require in the neighborhood of about one-half of one percent of caustic sod a, by weight, of oil charged to the still. Oils of high acid content will require a greater quantity of alkali in proportion. However, it may be said that the quantity of alkali used in practically all cases will usually range from one-half of one percent to two percent by weight of the oil distilled. The alkaline material, preferably caustic soda, may conveniently be introduced into the oil undergoing distillation in the form of an aqueous solution, although pulverized anhydrous caustic soda or soda ash and the like may be used if desired.

The application of the invention to the refining of all types of lubricating oils results in producing therein the highly desirable properties of good color, freedom from constituents of an acidic nature, and resistance to emulsification. However, the appli ration of the invention to the refining of naphthene base oils such as those derived from the crude petroleums produced in California and the Gulf Coastal fields of Texas and Louisiana may produce the greatest benetits. Such oils, when refined under normal conditions. are not suitable for the exacting requirements of steam turbine lubrication or for use in insulating high tension transformers or for service under like conditions due, to their tendency to oxidize or separate sludgy material. This tendency toward oxidation is apparently aided by impurities in the oil resulting from its previous refining treatment. However, it has been found that lubricating oils may be prepared from naphthene base oils in accordance with my invention which have the highest resistance toward oxidation thus far encountered in numerous tests made upon all classes and type of mineral lubricating oils.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and. scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

lVhat I claim is:

1. The process of treating and purifying petroleum lubricating oil which comprises agitating the oil with concentrated sulfuric acid at normal temperatures, separating the bulk of the acid and the sludge products of the reaction, substantially neutralizing the acid-treated oil and then distilling the oil under a subatmospheric pressure in the presence of an alkaline material.

The process of manufacturing hydrocarbon lubricating oil which comprises distilling the lighter fractions from a crude petroleum, agitating the residual oil with concentrated sulfuric acid, separating the hull: of the acid and sludge products of the reaction, substantially neutralizing the treated oil with an alkali and then distilling off a fraction of the treated oil under vacuum in the presence of an alkaline material.

3. The process of manufacturing hydrocarbon lubricating oil which comprises distilling the oil in the presence of an alkaline material and then treating the oil with concentrated sulfuric acid, separating the bulk of acid and sludge products of the reaction, substantially neutralizing the treated oil with an alkaline solution and then distilling the oil under a subatmospheric pressure in the presence of an alkaline material. 

